HD6417641 RENESAS [Renesas Technology Corp], HD6417641 Datasheet - Page 151

• Manufacturer Part Number: HD6417641
• Manufacturer: RENESAS [Renesas Technology Corp]

Every time an ALU arithmetic operation is executed, the DC, N, Z, V, and GT bits in DSR are
basically updated in accordance with the operation result. However, in case of a conditional
operation, they are not updated even though the specified condition is true and the operation is
executed. In case of an unconditional operation, they are always updated in accordance with the
operation result. The definition of a DC bit is selected by CS0 to CS2 (condition selection) bits in
DSR. The DC bit result is as follows:
Carry or Borrow Mode: CS[2:0] = 000: The DC bit indicates that carry or borrow is generated
from the most significant bit of the operation result, except the guard-bit parts. Some examples are
shown in figure 3.3. This mode is the default condition. When the input data is negative in a PABS
or PNEG instruction, carry is generated to add 1 to the LSB.
Operation Sequence Example
PADD X0, Y0, A0
Stage
MA/DSP
EX
+)
–)
ID
IF
Figure 3.3 DC Bit Generation Examples in Carry or Borrow Mode
0000
0000
0000 0001 0000 0000 0000 0000
0000
0000
0000 0000 0000 0000 0000 0000
Guard bits
Guard bits
Slot
Borrow is not detected
0000
0000
0000
0000
Carry is detected
Example 1
Example 3
MOVX.W @(R4, R8), X0
MOVX.W @R4+, X0
1111
0000
0000
0000
MOVX
1
Figure 3.2 Operation Sequence Example
1111
0000
0000
0000
Carry detecting point
Borrow detecting point
MOVX & PADD
1111
0000
0000
0000
MOVX
1111
0001
0001
0001
2
Previous cycle result is used.
MOVX & PADD
Addressing
3
(1)
+)
–)
1111
0011
0011
0000
0000
1111 1111 1111 1111 1111 1111
Guard bits
Guard bits
Addressing
1111
1111
1110 1000 0000 0000 0000
0000
0000
Carry is not detected
MOVX
Borrow is detected
Rev. 4.00 Sep. 14, 2005 Page 101 of 982
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Example 2
Example 4
0111
0001
0001
0001
MOVX & PADD
0000
0000
0000
0000
Carry detecting point
Borrow detecting point
0000
0000
0000
0000
5
Section 3 DSP Operation
0000
0000
0001
0010
REJ09B0023-0400
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